Regenerative braking for gas turbine systems

ABSTRACT

The present invention is directed to an energy storage system comprised of a heat block having a relatively high specific energy capacity. The heat block can be used, for example, with a regenerative braking system for gas turbine powered vehicles to improve fuel efficiency.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.12/405,934, filed Mar. 17, 2009, now U.S. Pat. No. 8,215,437, thatclaims the benefit of U.S. Provisional Application Ser. No. 61/037,039,filed Mar. 17, 2008, entitled “Regenerative Braking Method forVehicles,” the entirely of which are incorporated by reference herein.

FIELD

The present invention relates generally to a thermal energy storagesystem suitable for power systems using gas turbines and specificallyfor application to regenerative braking in gas-turbine powered vehicles.

BACKGROUND

The world requires ever-increasing amounts of fuel for vehiclepropulsion. Means of utilizing fuels needs to be accomplished moreefficiently and with substantially lower carbon dioxide emissions andair pollutants such as NOxs. For vehicles powered by gas turbines, a newmeans of energy storage can recover substantial amounts of energynormally discarded in braking

Gas turbines can be used in vehicles where they have the additionaladvantage of being highly fuel flexible and fuel tolerant. For example,gas turbines can be operated on a variety of fuels such as diesel,gasoline, ethanol, methanol, natural gas, biofuels and hydrogen. Theefficient utilization of gas turbines can be improved by a highspecific-energy storage means that can efficiently transfer stored heatenergy, acquired by a regenerative braking system, to a gas turbineengine when required.

There remains a need for a compact, high-capacity energy storage systemthat can be used in conjunction with gas turbine engines to improve theoverall fuel efficiency and reduce emissions.

SUMMARY

These and other needs are addressed by the various embodiments andconfigurations of the present invention which are directed generally toan efficient energy storage method compatible with gas turbines, andspecifically to energy storage systems for regenerative braking in gasturbine powered vehicles.

Vehicles that may be powered by gas turbine engines and a regenerativebraking system based on storing thermal energy include but are notlimited to trucks, cars, SUVs, locomotives, buses and off-road vehiclessuch as for example material haulage and dump trucks.

In a first embodiment, an energy storage system includes:

(a) a heat block in thermal communication with at least one an energysource, wherein the heat block is configured to store thermal energy;

(b) a thermally insulative enclosure surrounding the at least one heatblock; and

(c) a heat exchanger in thermal communication with the at least one heatblock to transfer heat from the heat block to a working fluid.

In a second embodiment, an energy storage system includes:

(a) a heat block, having a first energy storage capacity and a firststorage temperature, in thermal communication with an energy source,wherein the heat block is configured to store thermal energy;

(b) an intermediate storage block, having a second energy storagecapacity and a second storage temperature, in thermal communication withthe heat block, wherein at least one of the following is true:

-   -   (B1) the first energy storage capacity is equal to or greater        than the second energy storage capacity;    -   (B2) the first storage temperature is greater than the second        storage temperature; and    -   (B3) a melting point of the heat block is equal to or greater        than a melting point of the intermediate storage block; and

(c) a thermally insulative enclosure surrounding the heat block and theintermediate storage block.

The heat block (or heat blocks in thermal communication with each other)may be blocks of solid material or compressed granular material. Theheat block storage systems may be made in rectangular, square,cylindrical or spherical geometries. The heat blocks can be made of anappropriate material such as carbon (especially graphite), boronnitride, boron carbide, silicon carbide, silicon dioxide, magnesiumoxide, alumina and the like. These are materials that have high specificheats as well has high melting temperatures. Heat can be added to heatblock by any one of electrical heating, heat transfer by solidconductors or heat transfer by circulating fluids. Heat can be extractedfrom a heat block preferably using heat transfer by circulating fluids.The output heat transfer fluids can be used to deliver energy typicallythrough a heat exchanger to the working gas of a gas turbine.

An intermediate storage transfer block is typically used to temporarilystore heat energy at a lower temperature than the temperature of theprimary heat storage block and has the function of transferring heatenergy to a heat transfer fluid at a temperature compatible with itsheat exchanger materials. An intermediate storage transfer block may bemade of the same material as the main heat storage block or it may havea lower specific energy capacity and melting temperature than the mainheat storage block.

In a third embodiment, a heat block is used to recover energy from avehicle braking system. The regenerative braking system includes:

(a) a gas turbine engine;

(b) one or more of a plug-in to a power grid, an electrical generatorand a braking system, the a plug-in to a power grid generatingelectrical energy when the engine is not operating, the electricalgenerator generating electrical energy when the engine is idling and thebraking system generating electrical energy when braking; and

(c) a resistive grid to transform the electrical energy into thermalenergy by resistive dissipation;

(d) at least one heat block in thermal communication with the resistivegrid to absorb the thermal energy, and.

The heat block is in thermal communication with the at least one gasturbine engine.

This energy is stored in the heat block and, when required, can be usedto add heat energy through a heat exchanger to the working fluid of agas turbine engine for any number of gas turbine configurations so as toreduce the energy normally provided by a combustor or provide all of theenergy normally provided by a combustor.

In a preferred configuration of this embodiment, a heat block is used toprovide energy storage for an intercooled recuperated gas turbine systemfor a vehicle with a mechanical or hydraulic transmission, wherein apermanent magnet motor/generator is used to brake the vehicle by itsdrive shaft to provide regenerative braking energy to a heat block.

These and other advantages will be apparent from the disclosure of theinvention(s) contained herein.

The above-described embodiments and configurations are neither completenor exhaustive. As will be appreciated, other embodiments of theinvention are possible utilizing, alone or in combination, one or moreof the features set forth above or described in detail below.

The following definitions are used herein:

“At least one”, “one or more”, and “and/or” are open-ended expressionsthat are both conjunctive and disjunctive in operation. For example,each of the expressions “at least one of A, B and C”, “at least one ofA, B, or C”, “one or more of A, B, and C”, “one or more of A, B, or C”and “A, B, and/or C” means A alone, B alone, C alone, A and B together,A and C together, B and C together, or A, B and C together.

Dynamic braking is implemented when the electric motors are used ingenerator mode during braking to provide all or a portion of the brakingforce for a vehicle. The electrical energy generated is typicallydissipated in a resistance grid system.

Energy density as used herein is energy per unit volume (joules percubic meter).

An energy storage system refers to any apparatus that acquires, storesand distributes thermal, mechanical or electrical energy which isproduced from another energy source such as a prime energy source, aregenerative braking system, or any source of renewable or fuel-basedenergy. Examples are a heat block, a battery pack, a bank of capacitors,a compressed air storage system and a bank of flywheels or a combinationof storage systems.

An engine refers to any device that uses energy to develop mechanicalpower, such as motion in some other machine. Examples are dieselengines, gas turbine engines, microturbines, Stirling engines and sparkignition engines.

A heat block is a solid or granular volume of material with a high heatcapacity and high melting temperature to which heat can be added by oneof more of electrical resistive heating, inductive heating, solidconductors, or a heat transfer fluid, and from which heat can beextracted by a heat transfer fluid.

A hybrid vehicle combines an energy storage system, a prime power unit,and a vehicle propulsion system. A parallel hybrid vehicle is configuredso that propulsive power can be provided by the prime power source only,the energy storage source only, or both. In a series hybrid vehicle,propulsive power is provided by the energy storage unit only and theprime power source is used to supply energy to the energy storage unit.

A mechanical-to-electrical energy conversion device refers an apparatusthat converts mechanical energy to electrical energy. Examples includebut are not limited to a synchronous alternator such as a wound rotoralternator or a permanent magnet machine, an asynchronous alternatorsuch as an induction alternator, a DC generator, and a switchedreluctance generator.

A permanent magnet motor is a synchronous rotating electric machinewhere the stator is a three-phase stator, like that of an inductionmotor, and the rotor has surface-mounted permanent magnets. In thisrespect, the permanent magnet synchronous motor is equivalent to aninduction motor where the air gap magnetic field is produced by apermanent magnet. The use of a permanent magnet to generate asubstantial air gap magnetic flux makes it possible to design highlyefficient motors. For a common 3-phase permanent magnet synchronousmotor, a standard 3-phase power stage is used. The power stage utilizessix power transistors with independent switching. The power transistorsare switched in ways to allow the motor to generate power, to befree-wheeling or to act as a generator by controlling frequency.

Regenerative braking is the same as dynamic braking except theelectrical energy generated is recaptured and stored in an energystorage system for future use.

Specific energy capacity as used herein is energy per unit mass (joulesper kilogram).

A traction motor is a motor used primarily for propulsion such ascommonly used in a locomotive. Examples are an AC or DC induction motor,a permanent magnet motor and a switched reluctance motor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of heat capacity of graphite versus temperature.

FIG. 2 is a plot of specific energy of a carbon block versus blocktemperature.

FIG. 3 is a schematic of an insulated carbon block energy storagesystem.

FIG. 4 is a schematic of an alternate insulated carbon block energystorage system.

FIG. 5 is a schematic of an insulated carbon block energy storage systemwith intermediate storage.

FIG. 6 is a schematic diagram of the principal elements of aregenerative braking system for a vehicle.

FIG. 7 is a schematic diagram of a moderate temperature carbon blockenergy storage system for a gas turbine.

FIG. 8 is a plot of pressure versus temperature for a gas turbineprocess with energy storage.

FIG. 9 a and FIG. 9 b is a flow chart of a heat storage regenerativebraking system during vehicle propulsion.

FIG. 10 a and FIG. 10 b is a flow chart of a heat storage regenerativebraking system during vehicle braking

FIG. 11 shows another heat exchanger configuration for an energy storageblock and a gas turbine.

FIG. 12 shows yet another heat exchanger configuration for an energystorage block and a gas turbine.

DETAILED DESCRIPTION

In the book “Submarine Technology for the 21st Century”, varioustechnologies are discussed for non-nuclear submarines capable ofoperating for long periods (several hours to days) while underwater. Oneof these technologies is the use of a graphite heat block as a heatsource for a closed-cycle gas turbine power plant. In particular, theuse of a graphite block heated to 2,500° C. in an induction furnace isdescribed. An inert gas flows through the block, picks up heat, spinsthe turbine and returns to complete the loop.

The energy storage possible with this technology is substantially higherthan other forms of energy storage and, in particular, is compatiblewith gas turbines as a source of auxiliary energy.

Capacitors, inductors, some batteries and flywheels can release theirenergy at very high rates but typically at the expense of energy storagecapacity. Graphite at high temperatures has a specific energy capacitycomparable to chemical explosives and is a very compact form of energystorage compared to capacitors, inductors, flywheels and batteriescommonly used in regenerative braking energy storage systems.

In terms of specific energy capacity, the following table shows thetypical specific energy capacities associated with several energystorage technologies.

Energy Storage Technology Specific Energy Capacity (MJ/kg) Capacitors0.0004 to 0.001 Inductors - Room Temperature 0.001 Inductors - Cryogenic0.003 Homopolar Generator (flywheel) 0.0085 Energy Storage Batteries 0.2Graphite Heat Block at 1,500 K 2.0 Graphite Heat Block at 2,000 K 3.0Chemical Explosive (Octol) 4.8

Some Thermal Properties of Carbon

The properties of carbon make it useful for the collection and storageof thermal energy. These properties include: (1) a high heat capacity,especially at elevated temperatures; (2) a high melting point; (3) ahigh thermal conductivity; and (4) relatively low heat loss byradiation. Although a number of other materials, such as boron nitride,boron carbide, silicon carbide, silicon dioxide, magnesium oxide,tungsten carbide and alumina can be used for a heat block, a preferredform of material is carbon and a preferred form of carbon is graphite.The graphite may be synthetic or impure graphite or high-quality naturalgraphite and it may contain some mineral impurities. The use of highpurity natural graphite is preferred, for example graphite having apurity of from about 95% to about 99.9% by weight. Graphite having apurity of about 90% to about 99% by weight may be used. Graphite blocksmay be blocks of solid graphite or compressed granular graphite.Graphite blocks may be fabricated from a single block, or they maycomprise two or more smaller blocks which can be arranged in efficientthermal contact with adjacent blocks. Various forms of graphite and itsfabrication are discussed in U.S. Pat. No. 5,994,681 entitled “Apparatusfor Eddy Current Heating a Body of Graphite”.

FIG. 1 is a plot of constant pressure specific heat capacity of graphiteversus temperature. Specific heat capacity in joules perkilogram-degrees kelvin 102 is plotted against temperature in degreeskelvin 103 resulting in the specific heat capacity curve 101 which risesfrom about 0 at 0° K. and asymptotes after about 1,500° K. after toapproximately 2,000 J/kg-K. This data was obtained from page 4-108 ofthe American Institute of Physics Handbook, 3^(rd) Edition.

FIG. 2 is a plot of specific energy capacity of a typical high qualitygraphite block versus block temperature. Specific heat capacity injoules per kilogram 202 is plotted against temperature in degrees kelvin203 resulting in the specific energy capacity curve 201. The specificenergy capacity curve 201 is obtained by integrating the curve ofspecific heat from an initial temperature of 300° K. to 3,000° K. Forexample, a graphite block at 2,000 K will have a specific heat energycapacity of about 3 megajoules per kilogram (MJ/kg).

A Heat Block for Thermal Energy Storage

It is to be understood that a reference to carbon or graphite herein isintended to include other appropriate heat block materials such as forexample other forms of carbon, boron nitride, silicon carbide, alumina,tungsten carbide or the like.

FIG. 3 is a schematic of an insulated carbon block thermal energystorage system. A carbon block 301 is mounted using thermally insulatingstandoff struts 303 inside an insulating container 302. The spacebetween the carbon block 301 and the insulating container 302 is filledwith an inert gas such as argon or helium or a suitable reducing gas,preferably at ambient pressure. Alternately, the space may be filledwith an inert or reducing gas at very low pressures (for example as lowas about 100 kilopascals).

A source of energy 305 is connected to the heat block 301 by a thermallyconductive pathway 306. In the case of a thermal source of energy, thepathway might be a transfer fluid with a high heat capacity and thermalconductivity such as, for example, liquid sodium contained in a conduitmade of a material that does not react with carbon, such as, forexample, tungsten piping. The pathway could alternately be a thermallyconductive solid with a high thermal conductivity and a high meltingpoint such as for example tungsten rods. In the case of an electricalsource of energy, the pathway might be a plurality of electricallyconductive wires with high melting temperature such as, for example,tungsten wires arranged to form a resistive grid inside the heat block301. The addition of heat energy to the heat block can be interrupted atany time by disconnecting the energy source either mechanically (forsolid conduction or heat transfer fluids), electrically (for electricalconduction) or by slowing the rate of flow of heat transfer fluid fromthe source to the heat block.

The heat block 301 is connected to a heat exchanger 307 by a thermallyconductive pathway 306. The pathway is preferably a heat transfer fluidwith a high heat capacity and thermal conductivity. In oneconfiguration, the heat transfer fluid is a liquid such as sodiumcontained in a conduit made of a material that does not react withcarbon such as for example tungsten tubes. In another configuration, theheat transfer fluid is an inert gas such as for example argon or heliumor a reducing gas contained in a conduits made of a material that doesnot react with carbon such as for example tungsten tubes. Helium is apreferred transfer fluid since it can transport a given amount ofthermal energy at a lower temperature than an inert gas with a highermolecular weight such as argon. This is important when the heatexchanger 307 is comprised of materials that have a substantially lowermelting temperatures than graphite. The pathway 309 is a working fluidthat is used in a gas turbine or is used in another heat exchanger (notshown) to add heat to the working fluid in a gas-turbine. Interruptionof the supply of heat energy from the heat block to the gas turbine canbe accomplished at any time by disconnecting the heat block eithermechanically (for heat transfer fluids) or by slowing the rate of flowof heat transfer fluid from the heat block to the heat exchanger.

As can be appreciated, the flow of transfer fluid or electrical currentin pathway 306 can be regulated so that the temperature of the heatblock is kept below a first desired maximum temperature. Also, the flowof transfer fluid in pathway 308 can be regulated so that thetemperature of the heat exchanger 307 is kept below a second desiredmaximum temperature.

FIG. 4 is a schematic of an alternate insulated carbon block energystorage system. A carbon block 401 is mounted using thermally insulatingstandoff struts 403 inside an insulating container 402. The spacebetween the carbon block 401 and the insulating container 402 is filledwith an inert heat transfer fluid such as argon or helium or a suitablereducing gas, preferably at ambient pressure. A source of energy 405 isconnected to the heat block 401 by a thermally conductive pathway 406.The pathway 406 has the same description as the pathway 306 in FIG. 3.The addition of heat energy to the heat block can be interrupted at anytime by disconnecting the energy source either mechanically (for solidconduction or heat transfer fluids), electrically (for electricalconduction) or by slowing the rate of flow of heat transfer fluid fromthe source to the heat block.

The heat block 401 is connected to a heat exchanger 407 by a thermallyconductive pathway 406 which uses the same heat transfer fluid containedin the space between the carbon block 401 and the insulating container402. The conduit or conduits 408 are made of a material that has a highmelting point such as for example tungsten tubes. Helium is a preferredtransfer fluid since it can transport a given amount of thermal energyat a lower temperature than an inert gas with a higher molecular weightsuch as argon. This is important when the heat exchanger 407 iscomprised of materials that have a substantially lower meltingtemperatures than the heat block 401. The pathway 409 is a working fluidthat is used in a gas turbine or is used in another heat exchanger (notshown) to add heat to the working fluid of a gas-turbine. Interruptionof the supply of heat energy from the heat block to the gas turbine canbe accomplished at any time by disconnecting the heat block eithermechanically (for heat transfer fluids) or by slowing the rate of flowof heat transfer fluid from the heat block to the heat exchanger.

As can be appreciated, the flow of transfer fluid or electrical currentin pathway 406 can be regulated so that the temperature of the carbonblock is kept below a first desired maximum temperature. Also, the flowof transfer fluid in pathway 408 can be regulated so that thetemperature of the heat exchanger 407 is kept below a second desiredmaximum temperature.

FIG. 5 is a schematic of an insulated carbon block energy storage systemwith intermediate storage transfer capability. A carbon block 501 ismounted on thermally insulating standoff struts 503 inside anintermediate storage block 510 which, in turn, is contained inside aninsulating container 502. The space between the carbon block 501 and theintermediate storage block 510 is filled with an inert gas such as argonor helium or a suitable reducing gas, preferably at ambient pressure.Alternately, the space may be filled with an inert or reducing gas atvery low pressures (for example as low as about 100 kilopascals). As canbe appreciated, the intermediate storage block 510 and the insulatingcontainer 502 can also be separated by thermally insulating standoffstruts.

A source of energy 505 is connected to the heat block 501 by a thermallyconductive pathway 506 as described in FIG. 3. The heat block 501 isconnected to a heat exchanger 507 by a thermally conductive pathway 506also as described in FIG. 3. The addition of heat energy to the heatblock can be interrupted at any time by disconnecting the energy sourceeither mechanically (for solid conduction or heat transfer fluids),electrically (for electrical conduction) or by slowing the rate of flowof heat transfer fluid from the source to the heat block.

The advantage of this configuration is that the temperature in theintermediate storage transfer block 510 can be lower than thetemperature of the carbon block 501 by making the mass of theintermediate storage transfer block 510 higher than that of the carbonmain heat storage block or by controlling the amount of energytransferred to the intermediate block. An intermediate storage transferblock is typically used to temporarily store heat energy at a lowertemperature than the temperature of the primary heat storage block andhas the function of transferring heat energy to a heat transfer fluid ata temperature compatible with its heat exchanger materials. Anintermediate storage transfer block may be made of the same material asthe main heat storage block or it may have a lower specific energycapacity and melting temperature than the main heat storage block. Thelower temperature of the intermediate storage transfer block 510 may bemore compatible with the heat exchanger materials of a gas turbine. Theheat block 501 stores most of the thermal energy while the intermediatestorage transfer block 510 acts more as a transfer means and need nothave a large energy storage capacity. This configuration givesadditional control over the temperature of the heat transfer fluid thatmoves heat from the storage system to the heat exchanger of the gasturbine.

Interruption of the supply of heat energy from the intermediate storagetransfer block to the gas turbine can be accomplished at any time bydisconnecting the transfer block either mechanically (for heat transferfluids) or by slowing the rate of flow of heat transfer fluid from thetransfer block to the heat exchanger.

As can be appreciated, the flow of transfer fluid or electrical currentin pathway 406 can be regulated so that the temperature of the carbonheat storage block is kept below a first desired maximum temperature. Byproper choice of geometry, size and materials, the temperature of theintermediate transfer block can be maintained at a second temperaturethat is substantially lower than that of the main heat block. Further,the flow of transfer fluid in pathway 408 can be regulated so that thetemperature of the heat exchanger 407 is kept below a third desiredmaximum temperature.

The heat block storage systems described in FIGS. 3, 4 and 5 can be madein rectangular, square, cylindrical or spherical geometries. The heatblock can be made of an appropriate material such as carbon, graphite,boron nitride, boron carbide, silicon carbide, silicon dioxide,magnesium oxide, tungsten carbide, alumina and the like. These are solidmaterials that have high specific heats and thermal energy densities aswell has high melting temperatures.

The approximate properties of some materials suitable for the heat blockof the present invention are shown in the table below.

Graphite Boron Nitride Silicon Carbide Maximum Working 2,000 1,800 1,650Temperature (C.) Density (kg/m³) 2,250 1,900 3,100 Room TemperatureSpecific 712 1,610 750 Heat (J/kg-K) Room Temperature 24 30 120 ThermalConductivity (W/m-K)

It is preferable to utilize solid thermal storage systems at ambientpressures to avoid the need for high temperature seals and to maintainthe operational simplicity of the system.

Thermal insulation may be provided by any number of well-known thermallyinsulating materials. Alternately, the space between the heat block andits insulating container may be evacuated to minimize heat loss. Theinner surfaces of the insulating container may be polished to minimizeradiative heat loss. The insulating standoff struts may made from aceramic such as for example alumina, silica, silicon nitride, siliconcarbide, boron carbide, tungsten carbide and the like. As can beappreciated, direct contact between any of the carbon blocks and anoxidizing gas is to be avoided when the temperature of those gases issuch as to result in substantial oxidation of the heat blocks. Thetemperature at which such oxidation occurs depends on the purity of theheat block material but may be as low as about 600 C for impure graphitecarbon up to about 900 C for pure natural graphite. The heat transferfluid, if in contact with the heat block, may in the form of a gas orliquid or combination thereof, preferably is substantially free ofoxidants, especially oxygen and oxides, to avoid combustion of the heatblock. This is particularly preferred when the heat block is formed froma combustible substance, such as carbon. In most applications, the heattransfer fluid includes no more than about 5 mole % oxidants, even moretypically no more than about 1 mole % oxidants, and even more typicallyno more than about 0.1 mole % oxidants. The primary component of thefluid is an inert element or compound, such as a member of the Group 18of the Periodic Table of the Elements with helium being preferred,and/or a reducing element or compound, such as an alkali metal, alkalineearth metal, a transition metal, and other metals that have a gaseous orliquid phase, with alkali metals being preferred. Typically, the fluidincludes at least about 50 mole % of the primary component, even moretypically at least about 75 mole %, and even more typically at leastabout 95 mole %.

Thermal Energy Storage for Regenerative Braking in Gas Turbine Vehicles

FIG. 6 is a schematic diagram of the principal elements of aregenerative braking system for a vehicle using a gas turbine engine. Anopen cycle gas turbine engine 602 is shown with air input 611 and fuelinput 612. The fuel many be any of natural gas, diesel, gasoline,bio-diesel, ethanol, methanol, hydrogen or the like. The engine has anexhaust stream 613. The desired output of the engine is typicallymechanical power of a rotating shaft 605 which is typically connected toa mechanical or hydraulic transmission 603. For regenerative braking, apossible configuration is a motor 604 connected to shaft 606 on the sideof the transmission that is connected to the drive shaft and drivingwheels. The motor may be an induction motor, a permanent magnet motor orthe like. When the vehicle is under power, the motor 604 is disengagedfrom the drive shaft 606. When the vehicle is braking, the motor 604 isengaged with drive shaft 606 and acts as a retarder generator to providebraking action by producing an electrical output via a circuit comprisedof electrical conductors 621 and 622. These conductors transmitelectrical energy to a resistive grid embedded in the heat block 601where the electrical energy is transformed into heat by resistivedissipation. The resulting thermal energy is stored in heat block 601.This is similar to the dynamic braking grid employed on diesel-electriclocomotives except that the heat is stored in a heat block rather thanbeing dissipated into the surrounding air.

In another configuration, a regenerative braking system may be comprisedof small motors on some or all of the vehicle's axles. When the vehicleis under power, the motors are disengaged from the axles. When thevehicle is braking, the motors are engaged with the axles to act as aretarder generators to provide braking action by generating anelectrical output which is directed via electrical conductors to aresistive grid embedded in the heat block where, as before, theelectrical energy is transformed into heat by resistive dissipation. Theresulting thermal energy is stored in heat block.

In yet another configuration, a second motor (not shown) is positionedon output shaft 605 between the engine and the transmission. When thevehicle is stationary and idling, this motor can be engaged to generateelectrical energy from the idling engine. This electrical output isdirected via electrical conductors to a resistive grid embedded in theheat block where, as before, and the electrical energy is transformedinto heat in the heat block by resistive dissipation.

As an alternate regenerative braking system, the output shaft 605,transmission 603, drive shaft 606 and motor 604 may be replaced by amechanical-to-electrical energy conversion device, such as an electricalgenerator or alternator, and one or more traction motors such as used ondiesel-electric locomotives. In this system, themechanical-to-electrical energy conversion device supplies electricalenergy to an AC or DC electrical bus which in turn provides electricalenergy to the traction motors for propulsion or absorbs electricalenergy from the traction motors during braking The traction motor ormotors provide propulsive power to the wheels or, when braking, can beswitched to act as generators to provide braking action thereby supplingelectrical energy to a heat block via a resistive grid embedded in theheat block. As in a diesel-electric locomotive, the AC or DC electricalbus can be configured to provide electrical energy to a heat block whenthe vehicle is stationary and idling via the resistive grid embedded inthe heat block. When idling, the electrical power supplied to the AC orDC bus can be switched to the resistive grid.

The heat from the heat block 601 can be used to provide all or a portionof the heat energy to the working fluid of the gas turbine via a heatexchanger (not shown) inside engine 602. When required, the heat storedin the heat block 601 is transferred to the gas turbine engine 602 viatransfer fluid conduits 631 and 632 which transports heat to a heatexchanger in the engine 602 via conduit 632 and return the fluid to theheat block 601 via conduit 632. This process is described in FIG. 6 forthe example of an intercooled, recuperated gas turbine engine. As can beappreciated, other configurations of gas turbine engines can be used.These can include configurations that may or may not have intercooling,recuperation, reheating; may or may not utilize a free power turbine;and may have fewer or more stages of compression.

FIG. 7 is a schematic diagram of a regenerative braking system for avehicle with a gas turbine engine which uses a carbon block energystorage system operated at moderate temperatures (preferably in therange of about 1,500° C. to about 2,000° C.). This figure shows anintercooled, recuperated gas turbine engine which is comprised of a lowpressure compressor (LPC) 704, an intercooler apparatus (IC) 705, a highpressure compressor (HPC) 706 a recuperator 707, a combustor 708, a highpressure turbine (HPT) 709, a low pressure turbine (LPT) 710, a freepower turbine (FPT) 711 with output shaft 715 and a transmission 743connected to a drive shaft 713. A regenerative braking system is alsoshown and it is comprised of a braking motor 714, a heat energy storageblock 701 and a heat exchanger 702. Without a contribution from thestored heat energy in block 707, inlet air 731 (which may be controlledby a valve such as 703) is compressed by LPC 705, then cooled atapproximately constant pressure in IC 705, compressed by HPC 706 toapproximately maximum working pressure. The inlet air is heated bypassing through recuperator 707 and then heated to full workingtemperature by fuel energy added in combustor 708. The hot, highpressure working fluid then expands in HPT 709 powering HPC 706 viacoupling 742, further expands in LPT 710 powering LPC 704 via coupling741 and finally expanding in FPT 711 powering output shaft 715. Theexhaust gases are then passed through the hot side of recuperator 707giving up heat energy to the inlet air passing through the cool side ofrecuperator 707 before being vented 733 to the atmosphere possibly by avalve similar to inlet valve 703.

When the vehicle brakes, transmission 743 is disengaged and motor 714 isengaged to generate electrical energy via conductors 721 where it isdissipated in a resistive grid (not shown) embedded in heat block 701. Aheat transfer fluid is circulated between heat block 701 and heatexchanger 702 via fluid conduit 722 which passes through the hot side ofheat exchanger 702. A portion or all of the compressed inlet air heatedby recuperator 707 can now be passed through heat exchanger 702 to gainfurther energy and temperature at approximately constant pressure beforebeing injected into combustor 708. If the injected air is at the desiredtemperature for the combustor exit, no fuel need be added. If theinjected air is at a lower temperature than the desired temperature forthe combustor exit, an appropriate amount of fuel 732 is added via avalve similar to inlet valve 703. As can be appreciated, when heat isadded to the inlet air via heat exchanger 702, less fuel is required bythe combustor 708 than without regenerative braking capability.

Depending on the duty cycle of the vehicle, the regenerative brakingsystem described herein can have a modest or a large effect on theoverall efficiency of the gas turbine. For example, a delivery van orbus normally has a duty cycle with a lot of stops and starts and so aregenerative braking system could substantially increase overall fuelefficiency. On the other hand, a long haul Class 8 semi-trailer truckmay have a duty cycle with few stops and starts and so a regenerativebraking system would provide some increase overall fuel efficiency bycapturing energy from downhill travel or the occasional stop and gotraffic conditions.

As an example of how such a regenerative braking system can be installedon a Class 8 semi-trailer truck, a 330 kg heat block can be mounted, forexample, under or on top of the trailer. Flexible insulated heattransfer fluid lines can be connected from the heat block to the cab.These lines would continue into the cab's engine compartment to a smallheat exchanger mounted on the gas turbine engine. Such a heat block,operated between about 1,730 C and 1,230 C, can deliver a useablethermal energy equivalent of about 24 gallons of diesel fuel.

FIG. 8 is a plot of working fluid pressure versus temperature for a gasturbine process with energy storage. This figure shows working fluidpressure 801 versus working fluid temperature 802 as it moves betweenthe components of the engine. Assuming a working gas flow rate of about1 kg/s in the gas turbine engine of this example, the temperatureentering the cold side of the recuperator is about 230 C and theenthalpy is about 0.5 MJ. The temperature exiting the cold side of therecuperator is about 500° C. and the enthalpy is increased to about 0.78MJ. In this example, heat from the heat block is transported by heliumat a pressure compatible with the cold side of the heat exchanger and ata temperature of about 800° C. into the hot side of the heat exchangerand exits at about 700° C. from the hot side of the heat exchanger. Thetemperature of the working fluid entering the cold side of the heatexchanger is about 500° C. and the enthalpy is about 0.78 MJ. Thetemperature exiting the cold side of the heat exchanger is about 750° C.and the enthalpy is increased to about 1.03 MJ. The temperature enteringthe combustor is about 750° C. and the enthalpy is about 1 MJ. Thetemperature exiting the combustor is the desired 1,090° C. and theenthalpy is increased to its highest value of about 1.37 MJ. In thisexample, the recuperator has added about 0.28 MJ, the heat exchanger hasadded about 0.25 MJ and the fuel in the combustor has added about 0.34MJ per kg of working fluid.

Without the energy added by the regenerative braking system, the fuelenergy required is about 0.59 MJ per second. When energy is added fromthe heat block, the fuel energy required is about 0.34 MJ per second orabout a 42% reduction in fuel consumption.

The engine in this example is about a 300 kW gas turbine. In thisexample, air is input at 1 kg/s and helium is pumped at about 0.16 kg/sto provide the required heat energy from the energy storage heat block.The maximum temperature developed on the hot side of the heat exchangeris about 800° C. which is within the capability of common heat exchangermaterials.

As can be appreciated, the maximum temperature developed on the hot sideof the heat exchanger can be reduced if the helium flow rate to the heatexchanger is increased or the maximum temperature developed on the hotside of the heat exchanger can be increased if the helium flow rate tothe heat exchanger is reduced.

FIGS. 9 a and 9 b is an example of a flow chart for simple, automateddecision making for controlling power flow from a heat storage system toa gas turbine engine during vehicle propulsion. This cycle of decisionscan be executed continuously (for example every millisecond) orintermittently (for example every 1 second) or at intervals in betweenby a predetermined computer program or by a computer program thatadapts, such as for example, a program based on neural networkprinciples. As can be appreciated, many of the steps can be carried outin different sequences and some of the steps may be optional.

In FIG. 9 a, the automated cycle begins 901 and in the first step 902,the average temperature of the heat block is determined by any number ofwell-known means. This temperature is also used to determine the amountof heat energy in the heat block. In step 903, if there is insufficientheat energy in the heat block, then the decision 904 is made to not useenergy from the heat block to reduce fuel consumption in the gas turbineengine and the program is returned 905 to the start of the cycle 901. Instep 903, if there is sufficient heat energy in the heat block, then therecuperator outlet flow temperature and the desired combustor outletflow temperatures are determined in step 906. The recuperator outletflow temperature is determined by any number of well-known means. Thedesired combustor outlet flow temperature is determined by the poweroutput requirement of the gas turbine engine which will depend onwhether the engine is set to idle, 30% maximum power, 80% maximum powerof full power by the vehicle operator. Once recuperator outlet flowtemperature and the desired combustor outlet flow temperature aredetermined, the amount of heat that is desired to be added to therecuperator outlet flow can be determined in step 907. This can be anamount to bring the flow temperature up to the desired combustor outletflow temperature in which case no fuel is required. Alternately, it canbe an amount to bring the flow temperature up to a temperature betweenthe recuperator outlet flow temperature and the desired combustor outletflow temperature in which case some fuel is required for the combustor.

The flow chart of FIG. 9 a continues in FIG. 9 b as indicated. In step908, the heat transfer fluid flow rate on the hot side of the heatexchanger (item 707 in FIG. 7) is adjusted to provide the amount of heatdetermined in step 907. Then the fuel flow rate into the combustor isreduced in step 909 to provide enough additional heat to the flow toachieve the desired combustor outlet flow temperature which is measuredas in step 910. If the combustor outlet flow temperature is within anacceptable range (for example within 25 degrees Kelvin of the desiredtemperature), then the program is returned 905 to the start of the cycle901 (see FIG. 9 a). If the combustor outlet flow temperature is outsidean acceptable range, then in step 912, the combustor outlet flowtemperature is determined to be either too high or too low. If thetemperature is too high, then the program returns to step 909 where thefuel flow rate into the combustor is reduced by an amount required toreduce the combustor outlet flow temperature to within the acceptablerange. If the temperature is too low, then the program moves to step 913to determine the additional amount heat to be added to the outlet flowfrom the recuperator either by the heat exchanger or by increasing fuelflow rate or by a combination of both. In step 914, the proportion ofheat to be added to the outlet flow from the recuperator by increasingfuel flow rate or heat transfer fluid flow rate is determined. Theselected proportion will depend on an algorithm that accounts forseveral factors including for example how much heat is available fromthe heat block, how fast the heat transfer from the heat block can beadded and the like. In step 915, the increase in heat transfer fluidflow rate is determined to provide the portion of heat from the heatblock and in step 916, the increase in fuel flow rate is determined toprovide the portion of heat from the fuel supply. The program then movesback to step 910.

FIG. 10 a and FIG. 10 b is an example of a flow chart for simple,automated decision making for controlling power flow to a heat storagesystem from a gas turbine engine during vehicle braking In FIG. 10 a,the automated cycle begins 1001 and in the first step 1002, the averagetemperature of the heat block is determined by any number of well-knownmeans. This temperature is also used to determine the amount of heatenergy in the heat block. The next step 1003 is to activate the brakingmotor (item 714 in FIG. 7). In step 1004, the capacity of the heat blockto accept additional heat is estimated. If there is not sufficientcapacity remaining in the heat block, then all the electrical energyfrom the braking motor may be shunted as indicated in step 1005 to aresistive air grid that is exposed to air flow such as is known fordynamic braking in diesel-electric locomotives. The program is thenreturned 1006 to the start of the cycle 1001. Alternately, step 1005 cancause the vehicle to activate a standard mechanical braking system or acombination of a mechanical braking system and a resistive air grid suchas used in step 1005.

The flow chart of FIG. 10 a continues in FIG. 10 b as indicated. Ifthere is sufficient capacity remaining in the heat block, then anestimate is made of the excess capacity in step 1007 and a determinationis made in step 1008 on whether all or a portion of the electricalenergy from the braking motor may be added to the heat block. If thereis sufficient capacity in the heat block, all of the electrical energyfrom the braking motor can be added to the heat block and then theprogram is then returned 1006 to the start of the cycle 1001 (see FIG.10 a). If there is insufficient capacity in the heat block, a portion ofthe electrical energy from the braking motor can be added to the heatblock as in step 1011 and the remaining portion can be diverted as instep 1012 to a resistive air grid such as used in step 1005. The programis then returned 1006 to the start of the cycle 1001 (see FIG. 10 a).

FIG. 11 shows another heat exchanger configuration for an energy storageblock and a gas turbine. As shown in FIG. 7, the heat block 601transfers heat to the working fluid of a gas turbine via a heatexchanger 602 which can add heat in parallel to a stream of workingfluid from the recuperator or in series with the stream of working fluidfrom the recuperator, depending on the desired inlet temperature of thecombustor 608. In FIG. 11, the heat block 1101 transfers heat to theworking fluid of a gas turbine via a heat exchanger 1102 which is inseries with the stream of working fluid from the recuperator. Theconfiguration of FIG. 11 has fewer components than the configuration ofFIG. 7. The configuration of FIG. 11 may be more suitable, for example,for a vehicle with a duty cycle comprised of primarily stops and startssuch as a delivery vehicle or bus where the heat block always has aready supply of heat energy.

FIG. 12 shows yet another heat exchanger configuration for an energystorage block and a gas turbine system. In this configuration, a secondheat exchanger 1222 is used first to transfer heat from the heat blockusing a first heat transfer fluid via path 1222 to a second heattransfer fluid via path 1223 to heat exchanger 1202 which is typicallyan integral part of the gas turbine engine. This configuration allowsthe heat block to be maintained at a higher temperature and henceincreased heat storage capacity. The maximum temperature achieved inheat transfer fluid used in path 1223 is typically limited by thematerials used in heat exchanger 1202 which is preferably inside theengine. The maximum temperature achieved in heat transfer fluid used inpath 1222 can be higher since the materials used in heat exchanger 1222may require a much larger heat exchanger which can be mounted outsidethe engine near the heat block.

A number of variations and modifications of the invention can be used.As will be appreciated, it would be possible to provide for somefeatures of the invention without providing others. For example, theheat block storage system can be used with a small vehicle such as a carwherein the engine may be a closed cycle gas turbine engine. In thisconfiguration, thermal energy may be input into the resistive grid of aheat block via a plug-in electrical connection to a power grid while thevehicle is parked and augmented by a regenerative braking system whenthe vehicle is underway.

The present invention, in various embodiments, includes components,methods, processes, systems and/or apparatus substantially as depictedand described herein, including various embodiments, sub-combinations,and subsets thereof. Those of skill in the art will understand how tomake and use the present invention after understanding the presentdisclosure. The present invention, in various embodiments, includesproviding devices and processes in the absence of items not depictedand/or described herein or in various embodiments hereof, including inthe absence of such items as may have been used in previous devices orprocesses, for example for improving performance, achieving ease and\orreducing cost of implementation.

The foregoing discussion of the invention has been presented forpurposes of illustration and description. The foregoing is not intendedto limit the invention to the form or forms disclosed herein. In theforegoing Detailed Description for example, various features of theinvention are grouped together in one or more embodiments for thepurpose of streamlining the disclosure. This method of disclosure is notto be interpreted as reflecting an intention that the claimed inventionrequires more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment. Thus, the followingclaims are hereby incorporated into this Detailed Description, with eachclaim standing on its own as a separate preferred embodiment of theinvention.

Moreover though the description of the invention has includeddescription of one or more embodiments and certain variations andmodifications, other variations and modifications are within the scopeof the invention, e.g., as may be within the skill and knowledge ofthose in the art, after understanding the present disclosure. It isintended to obtain rights which include alternative embodiments to theextent permitted, including alternate, interchangeable and/or equivalentstructures, functions, ranges or steps to those claimed, whether or notsuch alternate, interchangeable and/or equivalent structures, functions,ranges or steps are disclosed herein, and without intending to publiclydedicate any patentable subject matter.

1. A vehicle system, comprising: (a) at least one gas turbine engine;(b) at least one of a plug-in to a power grid, an electrical generatorand a braking system, the a plug-in to a power grid generatingelectrical energy when the at least one gas turbine engine is notoperating, the electrical generator generating electrical energy whenthe at least one gas turbine engine is idling and the braking systemgenerating electrical energy when braking; (c) a resistive grid totransform the electrical energy into thermal energy by resistivedissipation; and (d) at least one heat block in thermal communicationwith the resistive grid to absorb the thermal energy, wherein the atleast one heat block is in thermal communication with the at least onegas turbine engine.
 2. The system of claim 1, wherein the electricalenergy is generated by a motor connected to a shaft in mechanicalcommunication with a transmission which is in mechanical communicationwith the at least one gas turbine engine, and wherein, in a first mode,the motor is disengaged from the shaft and produces substantially noelectrical energy and, in a second mode, the transmission is disengagedand the motor is engaged with the shaft and generates the electricalenergy in response to braking
 3. The system of claim 1 wherein theelectrical energy is generated by: (a) a first motor connected to afirst shaft in mechanical communication with a transmission which is inmechanical communication with the at least one gas turbine engine; and(b) a second motor connected to a second shaft in mechanicalcommunication with both the at least one gas turbine engine and thetransmission; and (c) wherein, in a first mode, the first and secondmotors are disengaged from the shafts and produce substantially noelectrical energy and, in a second mode, the second motor is engagedwith the second shaft and generates the electrical energy when thevehicle is stopped and idling and, in a third mode, the first motor isengaged with the first shaft and generates the electrical energy inresponse to braking
 4. The system of claim 1, wherein the electricalenergy is generated by one or more motors each connected to an axle inmechanical communication with the vehicle, and wherein, in a first mode,the one or more motors are disengaged from the axles and producesubstantially no electrical energy and, in a second mode, the one ormore motors are engaged with the axles and generate the electricalenergy in response to braking
 5. The system of claim 1 wherein the atleast one gas turbine is in communication with amechanical-to-electrical conversion device which is in electricalcommunication with an electrical bus which is electrical communicationwith one or more traction motors which are in mechanical communicationwith one or more axles and wherein the electrical energy is generated byat least one of the mechanical-to-electrical conversion device and oneor more of the traction motors, wherein, in a first mode, the one ormore traction motors produce substantially no electrical energy and, ina second mode, the one or more traction motors are operated as retardergenerators to generate the electrical energy in response to braking,and, in a third mode, the mechanical-to-electrical conversion devicegenerates the electrical energy.
 6. The system of claim 1, wherein aheat exchanger is in thermal communication with the heat block andtransfers thermal energy from the heat block to a working fluid andwherein the heated working fluid provides substantially all the powerfor a gas turbine engine.
 7. The system of claim 1, wherein the gasturbine engine comprises: a first low pressure compressor to compress aninput fluid to form a first input fluid at a first pressure; anintercooler apparatus to cool the first input fluid to a lower firsttemperature; a first high pressure compressor to compress the cooledfirst input fluid to form a second fluid at a second pressure higherthan the first pressure; a recuperator to heat the second input fluid toa higher second temperature; a heat exchanger in thermal communicationwith the heat block wherein the second input fluid passes through thecold side of the heat exchanger; a combustor to heat the second inputfluid to form a third input fluid having a third temperature higher thanthe first and second temperatures; a second high pressure turbine topower the first high pressure compressor in response to expansion of thethird input fluid; a second low pressure turbine to power the first lowpressure compressor in response to further expansion of the third inputfluid; and a free power turbine to power an output shaft in response tofurther expansion of the third input fluid, wherein the working fluid isthe second input fluid.
 8. The system of claim 7, wherein fuel issupplied to the combustor when the second input fluid is at atemperature less than the third temperature.